Tests - Intermittently failing saved search api tests [MJ-412]

We were using get_or_create to test for an exact saved search match - exact label, same frequency, exact email address, everything. The solution I found was to limit this to user, url, and case-insensitive email matching. If that fails, a new search is created.

The tests have been clarified slightly and `test_existing_search` has been updated to use the correct emails.